Keep header_ids option as nil

lib/commonmarker/config.rb

@@ -62,9 +62,9 @@ class << self
 
       def process_options(options)
         {
-          parse: process_parse_options(options[:parse]),
-          render: process_render_options(options[:render]),
-          extension: process_extension_options(options[:extension]),
+          parse: process_parse_options(options[:parse].dup),
+          render: process_render_options(options[:render].dup),
+          extension: process_extension_options(options[:extension].dup),
         }
       end
 

test/config_test.rb

@@ -45,4 +45,39 @@ def test_config_merges_directly
     # hardbreaks still work
     assert_equal("<p>aaaa<br />\nbbbb</p>\n", Commonmarker.to_html("aaaa\nbbbb", options: { render: { unsafe: false } }))
   end
+
+  def test_same_config_again
+    user_config = {
+      extension: {
+        header_ids: nil,
+      },
+    }
+
+    text = "# Heading-1"
+    expected = "<h1>Heading-1</h1>\n"
+
+    assert_equal(expected, Commonmarker.to_html(text, options: user_config))
+
+    # expect same result
+    assert_equal(expected, Commonmarker.to_html(text, options: user_config))
+  end
+
+  def test_render_and_to_html_with_same_config
+    user_config = {
+      extension: {
+        header_ids: nil,
+      },
+    }
+
+    text = "# Heading-1"
+    expected = "<h1>Heading-1</h1>\n"
+
+    doc = Commonmarker.parse(text, options: user_config)
+    # doc.walk do |node|
+    #   # do something
+    # end
+    doc.to_html(options: user_config)
+
+    assert_equal(expected, Commonmarker.to_html(text, options: user_config))
+  end
 end